Final answer:
Octavian, Mark Antony, and Lepidus formed the Second Triumvirate after Caesar's assassination, which led to Octavian's rise as the first Roman Emperor, Augustus.
Step-by-step explanation:
After Caesar's death, his heir grandnephew Octavian, his ally and assistant Mark Antony, and his cavalry commander Lepidus, joined forces to form the Second Triumvirate. This was a formal political arrangement recognized by the Senate, under which they shared the power of dictator in Rome following the demise of Julius Caesar. The Second Triumvirate was crucial in defeating the forces of Caesar's assassins at the Battle of Philippi and consolidating control over the Roman Republic. Eventually, Octavian and Mark Antony would contest for sole control of Rome's vast empire, leading to the end of the triumvirate and the rise of Octavian as the first Roman Emperor, Augustus.